Method for rendering digital radiographic images for display based on independent control of fundamental image quality parameters
A method of enhancing a digital image comprising: providing a digital image; decomposing the provided digital image into a multi-frequency band representation including a low frequency band image and multiple different high frequency band images; multiplying each of the high-frequency band images with a gain factor; summing together the unmodified low frequency band image and the modified high-frequency band images to produce a reconstructed digital image; and mapping the reconstructed digital image through a tone-scale look-up-table to map the reconstructed digital image to optical densities
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This invention relates in general to image enhancement in digital image processing and in particular, to a method of image enhancement to be used in a medical radiographic imaging system, such as a computed radiography system.
BACKGROUND OF THE INVENTIONIt is a common desire to enhance images acquired from imaging devices to improve their image quality. There are fundamental attributes that govern the image quality of a grayscale image. These attributes are the brightness of an image, the dynamic range of an image, the contrast of detail in an image (or detail contrast), the sharpness of edges in an image, and the appearance of noise in an image. It is beneficial to provide a system that enables direct and independent control of these attributes of image quality. Further a system, which enables the control of the detail contrast, sharpness, and noise appearance in a density dependent fashion is also beneficial.
U.S. Pat. No. 5,805,721, inventors P. Vuylsteke and E. Schoeters, entitled “Method and Apparatus for Contrast Enhancement”, issued Sep. 8, 1998 describes a multi-resolution method for enhancing contrast with increased sharpness that includes dynamic range compression, and enhancing contrast without remarkably boosting the noise component. The described invention enhances detail contrast and sharpness via a multi-resolution method and controls dynamic range compression with a gradation curve to map the processed image into the appropriate dynamic range for the display. Application of the gradation curve will impact both the apparent detail contrast and dynamic range of the displayed image. Hence, both the modifying functions of the multi-resolution processing and the shape of the gradation curve affect the detail contrast in the image. This requires that both be adjusted when setting the detail contrast in the image.
U.S. Pat. No. 5,978,518, inventors Oliyide et al., entitled “Image Enhancement in Digital Image Processing”, issued Nov. 2, 1999 and U.S. Pat. No. 6,069,979 (continuation-in-part of U.S. Pat. No. 5,978,518), inventor VanMetter, entitled “Method for Compressing the Dynamic Range of Digital Projection Radiographic Images”, issued May 30, 2000, describe a multi-resolution method for performing dynamic range modification and high-frequency enhancement (including detail contrast). The methods include a tone scale look-up-table that is used to map the image for display rendering. A tone scale look-up-table impacts the dynamic range and contrast of detail in an image. Hence, in this method, the dynamic range and detail contrast of the image depends on both the settings of the frequency modification and the parameters of the tone scale look-up table. It is desirable, instead to have a single set of parameters that control these attributes independently.
U.S. Pat. No. 6,072,913, inventor M. Yamada, entitled “Image Processing Method and Apparatus”, issued Jun. 6, 2000, describes a multi-resolution method for enhancing frequencies with dynamic range compression. The described invention requires the definition of many functions to control the performance of the algorithm. It does not disclose a set of parameters that directly and independently control all of the fundamental attributes of image quality.
Thus, there is a need for a method that can be applied to an image, the parameters of which provide direct and independent control of the above stated fundamental attributes of image quality.
SUMMARY OF THE INVENTIONAccording to the present invention, there is provided a solution to the problems and fulfillment of the needs discussed above by means of a method of digital image enhancement, especially image enhancement of medical diagnostic (radiographic) digital images.
According to a feature of the present invention, there is provided a method for enhancing an image: providing a digital image; decomposing the image into a multi-frequency band representation including a low frequency band image and multiple different high frequency band images; multiplying each of the high frequency band images with a gain factor; summing together the unmodified low frequency band image and the modified high-frequency band images to produce a reconstructed digital image: and mapping the reconstructed image through a tone scale look-up-table to map it to optical densities.
ADVANTAGEOUS EFFECT OF THE INVENTIONThe invention has the following advantages.
1. A method for independently controlling fundamental attributes of image quality of a digital image.
2. A method for controlling detail contrast, sharpness, and noise appearance as a function of log exposure of a digital image is provided.
3. A method for density-dependent control of detail contrast, sharpness and noise appearance of a digital image is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to
As shown further in
I′(i,j)=B0(i,j)+g1(B0(i,j))*B1(i,j)+g2(B0(i,j))*B2(i,j)+g3(B0(i,j))*B3(i,j)
If the bands are not manipulated, that is if g1(B0(i,j))=g2(B0(i,j))=g3(B0(i,j))=1.0, the reconstructed image I′ is equal to the original image I, i.e., I′(i,j)=I(i,j).
As shown in
about the reference density. The reference density maps the log exposure value that will remain invariant when the slope of the tone scale is varied. The brightness control is used to shift the mean density of the image. The brightness control defines the log exposure code value that is mapped via the tone scale to the reference density.
The amount of contrast in which the mid size detail in an image is rendered is defined as the detail contrast. In traditional screen film radiographic imaging systems, there is an inherent tradeoff between detail contrast and latitude (or range of log exposure that are rendered to unique densities). In these systems, if the contrast is increased, the latitude is decreased (or image dynamic range is increased). Likewise, if the latitude is increased, (or image dynamic range decreased) the detail contrast is decreased. The same is true if the image dynamic range and detail-contrast are controlled via a digital enhancement process (e.g., multi-resolution decomposition) in which the output of the process is mapped through a tone scale to render it to the display. Inherently, the tone scale also modifies both the dynamic range and detail contrast of an image. As shown in
In the embodiment of the present invention, shown in
also affects the dynamic range.
According to the present invention, the lowest band is not manipulated for dynamic range control; instead, the slope of the tone scale is used. The dynamic range control is defined as the slope of the tone scale, dynamicRange=dD/dx at the reference density. Increasing the dynamic range reduces the latitude while decreasing the dynamic range increases the latitude.
Manipulation of band B1(i,j) affects the detail contrast of the image. According to the present invention, band B1(i,j) is multiplied by the gain term g1(B0(i,j)) at multiplier 61. As previously discussed, the slope of the tone scale also affects the detail contrast of the image. To account for the fact that both the slope of the tone scale
and the gain term g1(B0(i,j)) affect the detail contrast, a detail contrast control is defined as a detailContrast(B0(i,j))=g1(B0(i,j))*(dD/dx).
By defining the dynamic range and detail contrast parameters in this way independent control of these attributes can be achieved. This is illustrated by
The controls for the sharpness of small features, sharpness(B0(i,j)), and very fine features, fineDetail(B0(i,j)), are defined as follows
To achieve the independent control of sharpness/blurring, it is found that controlling the gain ratio between the frequency bands is important. The sharpness(B0(i,j)) parameter provides control of the sharpness of small detail in an image, and the fineDetail(B0(i,j)) parameter provides an extra level of control over the sharpness of very fine detail in an image.
The gain terms that are used to manipulated the frequency bands, B1, B2, and B3 are derived from detail contrast, sharpness and fine detail controls respectively as follows
g1(B0(i,j))=detailContrast(B0(i,j))/dD/dx
g2(B0(i,j))=sharpness(B0(i,j))*g1(B0(i,j))
g3(B0(i,j))=fineDetail(B0(i,j))*g2(B0(i,j))
The present invention enables exposure dependent control of the detailContrast(B0(i,j)), sharpness(B0(i,j)), and fineDetail(B0(i,j)). The low band image B0(i,j) represents the average log exposure and serves as a map of exposure regions in an image. To achieve exposure dependent control of the image enhancement, the parameters are defined as a function of that band. Areas of the low band image where the code values are low correspond to the low exposure regions in the image (that is the low density or bright areas in the image). Areas where the code values are high correspond to high exposure regions in the image (that is the high density or dark areas in the image). This information can be used to provide exposure dependent control of detail contrast, sharpness of edges, and sharpness of fine detail and to improve the enhancement of the image.
As shown in
It will be evident to those skilled in the art that there are other useful functional forms that can be generated for the detailContrast(B0(i,j)), sharpness(B0(i,j)), and fineDetail(B0(i,j)) controls.
Another embodiment of the present invention is shown in
I′(i,j)=g3(I0(i,j))I(i,j)+(1−g1(I0(i,j)))I0(i,j)+(g1(I0(i,j))−g2(I0(i,j)))I1(i,j)+(g2(I0(i,j)−g3(I0(i,j)))I2(i,j)
This embodiment produces the same result as the method shown in
It is a preferred embodiment of this invention that the brightness and dynamic range parameters and the parameters for the detailContrast(B0(i,j)), sharpness(B0(i,j)), and fineDetail(B0(i,j)) functions be either entered directly at a user interface to the algorithm or automatically determined via an image analysis method.
Referring now to
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
Parts List
- 10 image acquisition unit
- 20 low-pass operator using filter K0
- 30 low-pass operator using filter K1
- 40 low-pass operator using filter K2
- 60,70,80 subtractor
- 61,71,81 multiplier
- 62,72,82 adder
- 90 tone scale process
- 91,92,93 gain terms
- 100 example tone scale function
- 200 low detail contrast and wide latitude image example
- 201 high detail contrast and narrow latitude image example
- 300 high-density lung field area
- 301 low-density diaphragm area
- 400-403 multiplier
- 501-503 adder
- 600 computer
- 601 memory
- 602 input device
- 603 display
- 604 processing unit
- 605 output device
- 606 control/data bus
- 607 transportable storage medium
- 608 storage media
Claims
1. A method of enhancing a digital image comprising:
- providing a digital image;
- decomposing the provided digital image into a multi-frequency band representation including a low frequency band image and multiple different high frequency band images;
- multiplying each of said high-frequency band images with a gain factor;
- summing together said unmodified low frequency band image and said modified high-frequency band images to produce a reconstructed digital image; and
- mapping said reconstructed digital image through a tone-scale look-up-table to map said reconstructed digital image to optical densities.
2. The method of claim 1 wherein said providing provides a digital medical image.
3. The method of claim 1 wherein said providing provides a digital radiological image acquired by one of a medical diagnostic imaging unit, a computed radiography unit, a direct digital radiography unit, and an x-ray film digitizer.
4. The method of claim 1 wherein said decomposing is effected by processing said provided digital image with a plurality of different low pass filter operators which operate to pass different low-pass images. Said low-pass images are used to generate said low-frequency band image and said multiple different high-frequency band images.
5. The method of claim 4 wherein said plurality of low pass filter operators use square wave filters.
6. The method of claim 4 wherein said plurality of different low pass filter operators use different filter kernel sizes to pass said different low-pass images.
7. The method of claim 6 wherein said plurality of different low pass filter operators include first, second and third pass filter operators having respective first, second and third kernels.
8. The method of claim 1 wherein said decomposing decomposes the provided digital image into four frequency bands as follows:
- a lowest frequency band image which represents large-sized features in the digital image;
- a low-to-mid frequency band image which represents mid-sized features in the digital image;
- a mid-to-high frequency band image which represents the small-sized features in the digital image; and
- a highest frequency band which represents very fine detail in the digital image.
9. The method of claim 8 including manipulating said lowest frequency band image to produce a dynamic range or latitude in said digital image.
10. The method of claim 8 including manipulating said low-to-mid frequency band image to produce a contrast effect without affecting the overall dynamic range of said digital image.
11. The method of claim 8 including manipulating said mid-to-high frequency band image to produce a sharpness or blurring effect of said small-sized features of said digital image.
12. The method of claim 8 including manipulating the highest frequency band image to produce a sharpness or blurring effect of very fine detail in said digital image.
13. The method of claim 1 wherein said mapping includes a brightness control for shifting the mean density of the digital image.
14. The method of claim 1 wherein said mapping further includes mapping the tone scale function to a standard gray scale display function for monochrome image presentation.
15. The method of claim 1 wherein in said mapping, said tone scale has slope at a reference density that defines dynamic range control and wherein increasing the dynamic range reduces latitude of said digital image, while increasing the dynamic range decreases the latitude to said digital image.
16. The method of claim 8 wherein said gain factor which multiplies said low-to-mid frequency band image is derived from a detail contrast control and said dynamic range control.
17. The method of claim 8 wherein said gain factor which multiplies said mid-to-high frequency band image is derived from a sharpness control and said gain factor which multiplies said low-to-mid frequency band image.
18. The method of claim 8 wherein said gain factor which multiplies said highest frequency band image is derived from a fine detail control and said gain factor which multiplies the mid-to-high frequency band image.
19. A method of enhancing a digital image comprising:
- providing a digital image;
- decomposing the provided digital image into a multi-frequency representation including a low frequency image and multiple different high frequency images;
- multiplying each of said high frequency images with a gain factor;
- summing together said unmodified low frequency image and said modified high frequency images to produce a reconstructed digital image; and
- mapping said reconstructed digital image through a tone scale loop-up-table to map and reconstructed digital image to optical densities.
20. The method of claim 8 wherein said gain factors which multiply said higher frequency bands are a function of said lowest frequency band image.
21. The method of claim 16 wherein said detail contrast control is a function of said lowest frequency band image (which represents average log exposure).
22. The method of claim 21 wherein the functional form of said detail contrast control is a piecewise linear curve with breakpoints.
23. The method of claim 22 wherein said breakpoints are first assigned in density and then mapped to log exposure breakpoints via said tone scale curve providing density dependent control of the detail contrast of said image.
24. The method of claim 17 wherein the said sharpness control is a function of said lowest frequency band image (which represents an average log exposure).
25. The method of claim 24 wherein the functional form of said sharpness control is a piecewise linear curve with breakpoints.
26. The method of claim 25 wherein said breakpoints are first assigned in density and then mapped to log exposure breakpoints via said tone scale curve providing density dependent control of the sharpness of small detail of said image.
27. The method of claim 18 wherein said fine detail control is a function of the lowest frequency band image (which represents an average log exposure).
28. The method of claim 27 wherein the functional form of said fine detail control is a piecewise linear curve with breakpoints.
29. The method of claim 28 wherein said breakpoints are first assigned in density and then mapped to log exposure breakpoints via said tone scale curve providing density dependent control of the sharpness of fine detail of said image.
30. The method of claim 15 wherein manipulation of said dynamic range control does not affect the detail contrast or sharpness of small of fine detail of said image.
31. The method of claim 16 wherein manipulation of said detail contrast control does not affect the overall dynamic range or sharpness of small or fine detail of said image.
Type: Application
Filed: Jul 24, 2003
Publication Date: Jan 27, 2005
Patent Grant number: 7266229
Applicant:
Inventors: Mary Couwenhoven (Fairport, NY), Robert Senn (Pittsford, NY)
Application Number: 10/625,964